Vinyl-type floor coverings have been known for a long time. Their composition is essentially based on vinyl chloride homopolymers or copolymers commonly called PVC.
Furthermore, products intended as floor coverings essentially produced from an acrylic resin or from olefin homopolymers or copolymers have recently appeared on the market for the purpose of replacing these PVC-type coverings, especially for environmental protection reasons.
These polymeric coverings, intended for covering floors, are called by those skilled in the art "resilient" polymeric coverings as opposed to coverings such as those made of ceramic and wood, which are not resilient.
Among polymeric coverings are the thermoplastic polymeric coverings mentioned above, but also certain thermosetting polymeric coverings comprising melamine resins used for producing floor coverings.
These floor coverings, whatever their nature, are intrinsically subjected to a great deal of traffic and consequently deteriorate quite quickly through wear.
In fact, this deterioration is essentially due to the scratchability of the covering by the rubbing of hard particles.
Various processes have consequently been proposed for improving the resistance of floor coverings by increasing the hardness of their surface, essentially by depositing a protective layer.
Most of the protective layers, more generally called "top coats", currently used are of the organic type and, in particular, are based on polyurethanes generally containing aliphatic polyisocyanates.
Such coverings may be applied using solutions, in organic phase, of one-part or two-part systems, of aqueous dispersions or of reactive systems having a solids content of 100%.
It may be mentioned that the solution systems are crosslinked by hydroxylated polyesters or polyethers, of which many types exist. Hydroxylated acrylic polymers are also used as a diisocyanate crosslinking agent. The crosslinking takes place in an oven and requires a catalyst.
As regards the polyurethane systems in aqueous phase, these are crosslinked by melamine resins or aziridines in an oven.
The solvent-free systems are intended to be dried under UV radiation. These are polyurethanes obtained from diisocyanates, from hydroxylated polyethers or polyesters and from hydroxylated acrylic monomers. They may be diluted with reactive polyacrylated monomers in order to adjust the application viscosity. Drying is extremely rapid, but does require the addition of photoinitiators.
Other systems have been used, such as:
hydrolysed alkyl silicate or organoalkoxy-silane+polyurethane elastomers, PA1 alkyd resin+polymethoxybutoxytrimethyl-siloxysilane+butoxylated melamine resin, PA1 ethoxylated melamine resin+epoxy resin+styrene-allyl alcohol copolymer, etc.
It should be noted that, in the literature, these top coats are always applied to vinyl-type floor coverings, that is to say those based essentially on PVC.
On the other hand, in the case of floor coverings based on other polymers, such as EVA (ethylene-vinyl acetate) copolymers, no specific mention of a protective layer has been made in the literature.
Nevertheless, the various techniques proposed come up against certain difficulties, the main ones of which are the scratchability and the loss of appearance, in particular the degree of gloss and of transparency, which defects are related to traffic. In addition, the adhesion of the protective layer to the substrate, which, in the case of a floor covering, is a resilient polymeric substrate, and the mechanical stability, between the deposit of organic material making up the protective or wear layer and the substrate itself, are often insufficient.